1. Field of the Invention
The present invention relates to a solid-state imaging device and a method for manufacturing the same.
2. Description of Related Art
In a CMOS solid-state imaging device, which is one of image sensors, generally light blocking is implemented by using a metal interconnect or an optical filter for the area that is desired to be free from light incidence thereon, such as a black-level reference pixel part and a peripheral circuit area.
In particular, if a film for implementing the light blocking is formed at the time of a step of forming a metal interconnect, the light-blocking film for the area that is desired to be free from light incidence thereon is formed at the same height as that of the interconnect layer because a CMOS logic process is applied as it is.
An example in which a light-blocking film for a black-level reference pixel part is formed in a step of forming a copper interconnect in a multilayer interconnect part will be described below with reference to FIG. 19, which is a schematic sectional view of a related-art CMOS image sensor.
As shown in FIG. 19, the related-art CMOS image sensor includes a light-receiving pixel part 112 and a black-level reference pixel part 113 that are formed on a semiconductor substrate 111 and formed of a photodiode. Furthermore, the related-art CMOS image sensor includes a multilayer interconnect part 114 formed on the light-receiving pixel part 112 and the black-level reference pixel part 113 (refer to e.g. Japanese Patent Laid-open No. 2006-294991).
The multilayer interconnect part 114 includes plural metal interconnects 130 (e.g. metal interconnects 131, 132, and 133) stacked sequentially from the semiconductor substrate 111 side along the thickness direction of the multilayer interconnect part 114, and an interlayer insulating film 140 that insulates the respective metal interconnects 130 from each other.
In the interlayer insulating film 140 (142) between the metal interconnect 130 (133) and the metal interconnect 130 (132) thereunder, a contact plug 151 that penetrates the interlayer insulating film 142 and connects the metal interconnect 133 to the metal interconnect 132 thereunder is formed.
On the top surface of an interlayer insulating film 145 formed to cover the top surface of the uppermost metal interconnect 130 (133), a pad 161 for electric connection to a peripheral circuit (not shown) or the like is formed by using e.g. aluminum (Al).
In the interlayer insulating film 145 between the pad 161 and the metal interconnect 133 (133c) directly beneath the pad 161, a contact plug 152 that penetrates the interlayer insulating film 145 and connects the pad 161 to the metal interconnect 133c is formed by using e.g. aluminum (Al).
The metal interconnect 133 (133a) opposed to the photodiode of the black-level reference pixel part 113 is formed as a light-blocking film that prevents light incidence on the photodiode region of the black-level reference pixel part 113.
For the CMOS image sensor, reduction in the thickness of the interconnect layer used as the light-blocking film is also simultaneously progressed because of miniaturization of the interconnect part due to reduction in the pixel size and because of the lowering of the interconnect height from the semiconductor substrate surface due to shortening of the optical path.
The reduction in the thickness of the interconnect layer will result in insufficient capability of the light-blocking film for preventing light incidence because the optical transmittance of a metal film exponentially decreases as the thickness thereof increases.